We propose to study the role of neuronal dysfunction in the pathogenesis of spinal cord injury. The cat spinal cord contusion model of injury will be used. Utilizing standard electrophysiological techniques, we intend to: 1) monitor the conductivity of spino-cortical tracts and vestibulospinal tracts, 2) assess segmental reflex responses elicited by peripheral stimulation, 3) record intracellularly from spinal motoneurons and extracellular evoked activity, 4) measure extracellular potassium ion activity with ion-selective microelectrodes, 5) correlate these neurophysiological findings with the histological extent of injury, blood flow changes, and biochemical parameters. We are particularly interested in determining the mechanisms leading to irreversible injury in spinal cord contusions. Because these mechanisms appear to take 2-3 hours to occur after injury, understanding of their nature may help in developing effective treatment regimens for spinal cord injury, especially in the first few hours. This study would be the first of its kind.